The CALGB Cytogenetic Core provides the infrastructure for giving CALGB investigators high quality cytogenetic data in AML, ALL, MDS, CML and CLL. These data are used in the group for 3 general purposes: a) to answer specific questions regarding the clinical and biologic significance of specific cytogenetic findings in these diseases; b) to provide information required to select the correct treatment study or protocol arm, and to allow appropriate analysis of therapy being investigated; and c) to provide information required for molecular genetic studies described elsewhere in this grant application (e.g., projects 1, 2, 3, and 5). As a result of information discovered (via CALGB protocol 8461) regarding the clinical significance of cytogenetics in AML and ALL, cytogenetics are currently used in stratifying patients for specific arms on our current front-line AML protocol in adults under the age of 60 years (CALGB 19808), and for selecting appropriate protocols for adults with ALL which differ based on cytogenetic findings (CALGB 10001, 10002, 10102). In CML (CALGB 10107) and MDS (CALGB 10105) disappearance of the cytogenetic abnormality will be used for monitoring outcome. Additionally, the integral relationship of cytogenetics with other leukemia correlative science studies (e.g., CALGB 9760, 9862, 20201, 20202) and most of the molecular studies performed through the CALGB Leukemia Tissue Bank (CALGB 9665) mechanism (see Core B of this grant application) make cytogenetic studies an essential component of almost all currently planned leukemia research. Cytogenetic data for AML, ALL and MDS are obtained via CALGB 8461, for CML via CALGB 29801 and for CLL via CALGB 20106 and 20203. The processing of submitted karyotypes and fluorescence in situ hybridization (FISH) results, cytogenetic data management and central review for these studies are done at The Ohio State University (OSU) under the direction of Dr. Clara D. Bloomfield.